Hydrocarbons methyl-branched

Ryoo, W., Webber, S.E. and Johnston, K.P. (2003) Water-in-carbon dioxide microemulsions with methylated branched hydrocarbon surfactants. Industrial and Engineering Chemistry Research, 42 (25), 6348-6358. 

Biosynthesis of methyl branched hydrocarbons of the German cockroach Blattella germanica (L.) (Orthoptera, Blattellidae). Insect Biochemistry 20 149-156. 

Charlton R. E. and Roelofs W. L. (1991) Biosynthesis of a volatile, methyl-branched hydrocarbon sex pheromone from leucine by Arctiid moths (Holomelina spp.). Arch. Insect Biochem. Physiol. 18, 81-97. 

The soluble and a unique microsomal fatty acid synthase (FAS) which are involved in producing the 18-carbon fatty acyl precursors to hydrocarbons have been purified to homogeneity and characterized (Gu et al., 1997). It appears that the soluble FAS synthesizes the straight chain fatty acids involved in n-alkane and alkene formation, whereas the microsomal FAS produces the precursors for the methyl-branched hydrocarbons (Blomquist et al. 1995). 

Evidence for a microsomal FAS in methyl-branched hydrocarbon formation... 

A microsomal FAS was implicated in the biosynthesis of methyl-branched fatty acids and methyl-branched hydrocarbon precursors of the German cockroach contact sex pheromone (Juarez et al., 1992 Gu et al., 1993). A microsomal FAS present in the epidermal tissues of the housefly is responsible for methyl-branched fatty acid production (Blomquist et al., 1994). The housefly microsomal and soluble FASs were purified to homogeneity (Gu et al., 1997) and the microsomal FAS was shown to preferentially use methylmalonyl-CoA in comparison to the soluble FAS. GC-MS analyses showed that the methyl-branching positions of the methyl-branched fatty acids of the housefly were in positions consistent with their role as precursors of the methyl-branched hydrocarbons. 

Figure 8.5 Steps in the biosynthesis of methyl-branched hydrocarbons in the housefly.

Chase J., Jurenka R. J., Schal C., Halamkar P. P. and Blomquist G. J. (1990) Biosynthesis of methyl branched hydrocarbons in the German cockroach Blattella germanica (L.) (Qrthoptera, Blattellidae). Insect Biochem. 20, 149-156. 

Guo L., Quilici D. R, Chase J. and Blomquist G. J. (1991) Gut tract microorganisms supply the precursors for methyl-branched hydrocarbon biosynthesis in the termite, Zootermopsis nevadensis. Insect Biochem. 21, 327-333. 

The rationale used in the interpretation of the mass spectra of methylalkanes has been presented in several reports 2- vs. 4-methylalkanes (Baker et al., 1978 Scammells and Hickmott, 1976 McDaniel, 1990 Bonavita-Cougourdan et al., 1991) 2,X- and 3,X-dimethylalkanes (Nelson et al., 1980 Thompson et al., 1981) and internally branched mono-, di- and trimethylalkanes (Blomquist et al., 1987 Pomonis et al., 1980). In the majority of reports, identification is based on GC and MS data, but the conclusions are not confirmed with standards or synthesis of the proposed structures. However, there are reports of chemical ionization (Howard et al., 1980) and electron impact of synthetic methyl-branched hydrocarbons (Carlson et al., 1978, 1984 Pomonis et al., 1978, 1980) and these have been very useful in confirming mass spectral fragmentation patterns with chemical structures. 

A 13C NMR study of methyl-branched hydrocarbon biosynthesis in the housefly. 

Katritzky, A. R. and Chen, K. (2000). QSPR correlation and predictions of GC retention indexes for methyl-branched hydrocarbons produced by insects. Anal. Chem., 72, 101-109. 

Figure 3.4 Biosynthetic pathway for internally methyl-branched hydrocarbons.

Long-chain methyl-branched hydrocarbons are the main components of the cuticular hydrocarbons in T. ni larvae (98%), pupae (98%) and adults (74%) and in S. eridania larvae (70%), pupae (75%) and adults (65%) (Guo and Blomquist, 1991), although large differences exist in their synthesis and transport to the cuticle throughout development. Immediately after a larval molt and during the feeding stages of the last two larval instars, hydrocarbons are actively synthesized and transported to the surface of the cuticle. 

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